This invention relates to a free-radical polymerization process for the production of branched xcfx89-unsaturated polymers (macromonomers) of general structure 1 based on monosubstituted vinyl monomers. 
The synthesis of macromonomers based on monosubstituted monomers has previously been achieved by the use of addition-fragmentation chain transfer agents. For example, by polymerization of an acrylate monomer in the presence of an allyl sulfide chain transfer agent (Rizzardo et al, Macomol. Symp., 15 1996, 111, 1). The synthesis of macromonomers has also been achieved by copolymerization of a monosubstituted monomer with an alpha-methylvinyl monomer, e.g., a methacrylate monomer, in the presence of a cobalt catalytic chain transfer agent. See, for example, WO 9731030. The process of the current invention does not require added reagents other than the polymerization initiator.
Polymerizations of various monomers (in particular, acrylic monomers) have previously been performed where reaction conditions have been chosen to maximize conversion and control molecular weight. For example, U.S. Pat. No. 4,546,160 describes a process for synthesizing polymers based on acrylic and methacrylic monomers where reactions are carried out at high reaction temperatures to limit molecular weight. However, no attention was paid to the design of reaction conditions to optimize the macromonomer purity or the branch structure.
U.S. Pat. No. 5,710,227 describes a synthesis of macromonomers based on monomers of acrylic acid and its salts. The process is performed at high reaction temperatures (typically  greater than 225xc2x0 C.) and does not describe the conditions necessary to control the purity of the macromonomer or the extent of branch formation. Furthermore, patentees report that macromonomer purity decreases as the polymerization temperature drops below 200xc2x0 C. The process is further restricted to polymers containing monomers of acrylic acid and its salts.
In conventional practice, when polymerizations are carried out at high reaction temperatures, these are typically carried out under conditions where there is a high flux of initiator-derived radicals. These conditions are unsuited for high purity macromonomer synthesis. The process disclosed herein sets out guidelines whereby the molecular weight of the macromonomer and the degree of branching in the macromonomer can be controlled. In the process described herein high purity ( greater than 90%) macromonomers are prepared at any polymerization temperature including temperatures below 100xc2x0 C. The process described herein can be applied to the preparation of xcfx89-unsaturated homopolymers of acrylates, styrene and vinyl esters. Furthermore, the process discloses guidelines for the preparation of high purity xcfx89-unsaturated random copolymers based on one or more monosubstituted vinyl monomers or based on one or more alpha-substituted vinyl monomers.
This invention is directed to a process for the synthesis of polymers of the general formula (1): 
comprising
(A) contacting:
(a) CH2xe2x95x90CHY;
(b) optionally, CH2xe2x95x90CXB;
(c) free radicals, produced from a free radical source;
wherein:
X is independently selected from the group consisting of halogen, or optionally substituted C1-C4 alkyl wherein the substituents are independently selected from the group consisting of hydroxy, alkoxy or aryloxy (OR), carboxy, acyloxy or aroyloxy (O2CR), alkoxy- or aryloxy-carbonyl (CO2R);
Y is independently selected from the group consisting of R, CO2H, CO2R, COR, CN, CONH2, CONHR, CONR2, O2CR, OR or halogen;
B is selected from the group consisting of R, CO2H, CO2R, COR, CN, CONH2, CONHR, CONR2, O2CR, OR, halogen or a polymer chain;
R is selected from the group consisting of optionally substituted C1-C18 alkyl, C2-C18 alkenyl, aryl, heterocyclyl, aralkyl, alkaryl wherein the substituents are independently selected from the group that consists of epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and salts), sulfonic acid (and salts), alkoxy- or aryloxy-carbonyl, isocyanato, cyano, silyl, halo, and dialkylamino;
Z is selected from the group consisting of H and a free radical initiator-derived fragment of optionally substituted alkyl, cycloalkyl, aryl, aralkyl, alkaryl, organosilyl, alkoxyalkyl, alkoxyaryl, hydroxy, hydroperoxy, alkylperoxy, alkoxy, aroyloxy groups wherein substituent(s) are selected from R, OR, O2CR, halogen, CO2H (and salts), CO2R, CN, CONH2, CONHR, CONR2, sulfate, 
mxe2x89xa71;
nxe2x89xa70;
pxe2x89xa70;
and when one or both of m and n are greater than 1, the repeat units are the same or different;
the [CH2xe2x80x94CUY]p moiety contains branch point, U, and is derived from structure (1) whereby U is of random structure (2): 
(B) controlling polymer quality by adjusting the following variables:
(i) increasing the proportion of vinyl terminated polymer by increasing the molar ratio of (a)/(b);
(ii) increasing the proportion of vinyl terminated polymer by decreasing the molar ratio of (c)[(a)+(b)];
(iii) controlling the degree of branching (value of p) as follows:
(d) decreasing p by increasing temperature;
(e) decreasing p by decreasing monomer concentration;
(f) increasing p by increasing conversion;
(iv) controlling the molecular weight of the polymer as follows:
(g) decreasing molecular weight by decreasing monomer concentration; and
(h) decreasing molecular weight by increasing temperature.
The preferred proportion of vinyl terminated polymer is xe2x89xa750 percent, more preferably, greater than 70 percent. The preferred degree of branching is, on average, xe2x89xa610 branches per chain. The preferred degree of polymerization (m+n+p) is from 1 to about 500.
We have found that macromonomers (1) can be synthesized by conducting a polymerization of monosubstituted monomer(s) with appropriate choice of reaction conditions. Monomers CH2xe2x95x90CHY and CH2xe2x95x90CXB are polymerizable or copolymerizable monomers. As one skilled in the art would recognize, the choice of monomers is determined by their steric and electronic properties. The factors which determine polymerizability and copolymerizability of various monomers are well documented in the art. For example, see: Greenley, in Polymer Handbook 3rd Edition (Brandup and Immergut, Eds.) Wiley, N.Y., 1989 p II/53.
Preferred monosubstituted monomers (CH2xe2x95x90CHY) are one or more of the following: methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, functional acrylates selected from glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), diethylaminoethyl acry late, triethyleneglycol acrylate, N-tert-butyl acrylamide, N-n-butyl acrylamide, N-methylol acrylamide, N-ethylol acrylamide, vinyl benzoic acid (all isomers), diethylamino styrene (all isomers), p-vinyl benzene sulfonic acid, trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, diethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate, vinyl acetate, and vinyl butyrate, vinyl chloride, vinyl fluoride, vinyl bromide and propene.
Preferred disubstituted monomers CH2xe2x95x90CXB are one or more of the following: methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), diethylaminoethyl methacrylate, triethyleneglycol methacrylate, trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, tributoxysilypropyl methacrylate, dimethoxymethylsilylpropyl methacrylate, diethoxymethyl-silylpropylmethacrylate, dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropyl methacrylate, dibutoxysilylpropyl methacrylate, disopropoxysilylpropyl methacrylate, itaconic anhydride, itaconic acid, methacrylamide, N-tert-butyl methacrylamide, N-n-butyl methacrylamide, N-methylol methacrylamide, N-ethylol methacrylamide, alpha-methyl styrene, alphamethylvinyl benzoic acid (all isomers), diethylamino alphamethylstyrene (all isomers) and isobutylene.
The source of initiating radicals can be any suitable method of generating free radicals such as the thermally induced homolytic scission of a suitable compound(s) (thermal initiators such as peroxides, or azo compounds), the spontaneous generation from monomer (e.g., styrene), redox initiating systems, photochemical initiating systems or high energy radiation such as electron beam, X- or xcex3-radiation. The initiator should also have the requisite solubility in the reaction medium and monomer mixture.
Thermal initiators are chosen to have an appropriate half-life at the temperature of polymerization. These initiators can include one or more of the following compounds: 2,2xe2x80x2-azobis(isobutyronitrile), 2,2xe2x80x2-azobis(2-cyano-2-butane), dimethyl 2,2xe2x80x2-azobisdimethylisobutyrate, 4,4xe2x80x2-azobis(4cyanopentanoic acid), 1,1xe2x80x2-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)-2-cyanopropane, 2,2xe2x80x2-azobis[2-methyl-N-(1,1)-bis(hydoxymethyl)-2-hydroxyethyl]propionamide, 2,2xe2x80x2-azobis[2-methyl-N-hydroxyethyl)]-propionamide, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramidine) dihydrochloride, 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramine), 2,2xe2x80x2-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide), 2,2xe2x80x2-azobis(2-methyl-N-[1,1-bis(hydroxymethyl) ethyl]propionamide), 2,2xe2x80x2-azobis[2-methyl-N-(2-hydroxyethyl) propionamide], 2,2xe2x80x2-azobis(isobutyramide) dihydrate, 2,2xe2x80x2-azobis(2,2,4-trimethylpentane), 2,2xe2x80x2-azobis(2-methylpropane), t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butylperoxy isobutyrate, t-amyl peroxypivalate, t-butyl peroxypivalate, di-isopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dicumyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, potassium peroxydisulfate, ammonium peroxydisulfate, di-t-butyl hyponitrite, dicumyl hyponitrite, cumyl hydroperoxide, t-butyl hydroperoxide.
While not wishing to be limited by any particular mechanism, it is believed that the process for macromonomer formation occurs as summarized in Scheme 1 and involves abstraction of a methine backbone hydrogen to give a radical of structure 3. Such chain transfer to polymer in acrylate polymerization is known (Lovell et al, Polym. Commun., 1991, 32, 98). However, the art would suggest that this process leads to formation of a branched polymer. We provide a set of conditions whereby formed radical 3 undergoes fragmentation to give a macromonomer and a new propagating species. 
Abstraction of a hydrogen from the backbone can, in principle, occur by either an intermolecular (transfer to polymer) or intramolecular (backbiting) process. The mechanism of backbone hydrogen abstraction by backbiting is shown in Scheme 2. This mechanism best accounts for the observed manner in which molecular weight varies with conversion (see Example 1). In this mechanism, two possible fragmentation routes exist. In principle, fragmentation can occur by either pathway A or pathway B leading to trimer macromonomer 4 (path A) or dimeric propagating radical 5 (path B). 
Under the conditions of the claimed process, if all radicals 3 (formed by any mechanism) undergo fragmentation, then the molecular weight of the polymer will be determined by the incidence of backbone abstraction. In the case of ethylene polymerization, it is known that high reaction temperatures favor backbiting. A similar situation is likely to apply in acrylate polymerization. Consequently, high reaction temperatures will increase the incidence of backbone methine hydrogen abstraction and increase the incidence of fragmentation. This has the overall effect of decreasing the molecular weight of the polymer (see Example 7). Similarly, lower monomer concentration reduces the propagation rate of polymerization providing an opportunity for an increase in the incidence of backbone hydrogen atom abstraction and hence fragmentation. As a consequence, lower molecular weights are observed (see Examples 10 and 11).
To summarize, control over molecular weight can be obtained by: (a) controlling the reaction temperature. A higher reaction temperature will give a lower molecular weight. Using the process described herein, macromonomers have been prepared at polymerization temperatures of 60xc2x0 C. (see Example 9, entry 2). Preferably, the polymerization temperature should be above 80xc2x0 C. (see Example 9, entry 1) and most preferably above 100xc2x0 C. (see Example 4, entry 3); and by (b) controlling the monomer concentration. A lower monomer concentration will give a lower molecular weight.
For polymerizations carried out at high temperatures the experimental results indicate fragmentation of radicals 3 dominates over bimolecular reaction with monomer even with relatively high monomer concentrations. Compare the results in Example 10 and Example 11 where lower molecular weights are obtained at 170xc2x0 C. (Example 11) compared with 150xc2x0 C. (Example 10). If lower reaction temperatures are employed there will be competition between fragmentation of radical 3 and reaction of radical 3 with monomer. The result is a polymer with a higher degree of branching for lower reaction temperatures (see Example 12). Furthermore, by increasing the monomer concentration the rate of the bimolecular reaction with radical 3 will increase giving rise to polymers with a higher degree of branching (see Example 13). The branched product can nonetheless still be a macromonomer. As the conversion to macromonomer increases, there is a greater likelihood that macromonomer will react giving a polymer with a higher degree of branching (see Example 14).
To summarize, the degree of branching can be controlled by: (a) controlling the reaction temperature. Higher reaction temperatures give a lower degree of branching; (b) adjusting the monomer concentration. A lower monomer concentration leads to a lower degree of branching; (c) the degree of conversion of monomer to polymer. The degree of branching can be increased by increasing the degree of conversion of monomer to polymer.
The macromonomers formed by the process of the present invention are likely to be reactive under the conditions of the experiment. However, the initial product is another radical of structure 3 and under the preferred reaction conditions these radicals will most likely undergo fragmentation. This process thus does not lead to impurity formation. The reaction offers some opportunity for chain length equilibration. Thus, these polymerizations can give narrower polydispersities than would otherwise be observed.
It is important in designing the reaction conditions to use an initiator concentration (radical flux) such that the number of chains formed by chain termination processes (i.e., combination, disproportionation) are small with respect to those resulting in macromonomer formation.
Macromonomer purity will in part be determined by the initiator concentration and the rate of generation of initiator-derived radicals which in turn determines the kinetic chain length (the length of polymer chain that would be formed in the absence of chain transfer).       Maximum    ⁢          xe2x80x83        ⁢    purity    =                                                        (                              moles                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                polymer                ⁢                                  xe2x80x83                                ⁢                formed                            )                        -                                                            (                          moles              ⁢                              xe2x80x83                            ⁢              initiator              ⁢                              xe2x80x83                            ⁢              derived              ⁢                              xe2x80x83                            ⁢              radicals                        )                                      (              moles        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        polymer        ⁢                  xe2x80x83                ⁢        formed            )      
moles polymer formed=(grams monomer converted)/(MW of polymer)
moles initiator derived radicals (moles of initiator consumed xc3x972)xc3x97initiator efficiency.
The acceptable range of initiator concentrations to give a required purity of macromonomer depends on the molecular weight of the macromonomer. The above expression requires that there be no transfer to monomer, solvent, initiator, etc. If these occur, then the purity will be lower. The preferred initiator concentration relative to monomer is less than 1 mol percent, more preferably, less than 0.1 mol percent.
If the mechanism of macromonomer formation involves intermolecular abstraction from polymer (rather than backbiting) there will also be up to an equivalent of non-macromonomer product of structure 6 formed the observation that macromonomer purity is  greater than 90% under the optimal conditions suggests that this pathway is of lesser importance. 
Thus, in general, macromonomer purity is increased by decreasing the molar ratio of initiator to total monomer(s) (see Example 4).
The mechanisms and general improvement conditions highlighted thus far will also apply in copolymerizations of monosubstituted vinyl monomers (e.g., acrylates, vinyl esters, styrene, and the like) with other monosubstituted vinyl monomers (see Examples 15, 16, 23 to 26). In examples of copolymers prepared with more than one monosubstituted vinyl monomer, macromonomers with more than one type of end group will be obtained. For example, copolymerizing butyl acrylate with styrene under the conditions specified in the present invention will give xcfx89-unsaturated polymers possessing BMA derived end groups 7 and AMS derived end groups 8 (see Example 15 for 1H-NMR). 
The mechanisms and general improvement conditions highlighted thus far will also apply in copolymerizations of monosubstituted vinyl monomers (e.g., acrylates, vinyl esters, styrene, and the like) with other alpha-substituted vinyl monomers. In examples of copolymers prepared with one or more alpha-substituted vinyl monomer(s), xcfx89-unsaturated polymers are formed, possessing vinyl end groups derived from the monosubstituted vinyl monomers (see Examples 17 to 19, 27, 28). Under the disclosed conditions of the claimed process, the abstraction of a hydrogen atom from the backbone can not occur from the alpha-substituted monomer unit, it can only occur from the monosubstituted monomer unit. This gives rise to a radical of general structure 9 which is likely to fragments as shown in Scheme 3. 
This will lead to macromonomer bearing an end group derived from the monosubstituted vinyl monomer. This is in contrast to the disclosure in WO 97/31030 where the xcfx89-unsaturated polymers have end groups derived exclusively from the alpha-substituted vinyl monomer.
Furthermore, in examples of copolymers prepared with one or more alpha-substituted vinyl monomer(s), the purity of the formed xcfx89-unsaturated polymers will depend on the relative amount of alpha-substituted vinyl monomer(s) used (see Examples 17 to 19). As the relative amount of alpha-substituted vinyl monomer units increase in the polymer chain, there is less likelihood of backbone hydrogen atom abstraction. This has the effect of increasing molecular weight of the polymer and as such will increase the likelihood of the propagating radical being involved in termination processes leading to dead polymer and thus decrease the purity of the formed macromonomer.
In copolymers composed of monosubstituted vinyl monomer(s) and alpha-substituted vinyl monomer(s), the purity of the copolymer macromonomer can be affected by the relative amount of alpha-substituted vinyl monomer(s). As the proportion of alpha-substituted vinyl monomer(s) decreases, purity of the copolymer macromonomer increases.
In an extension of this process, the disclosed conditions are used to prepare xcfx89-unsaturated homopolymers of general structure 10 containing one type of vinyl end group based on the monosubstituted vinyl monomer. 
In a further extension of this process, xcfx89-unsaturated copolymers of general structure 11 composed of one monosubstituted vinyl monomer and one or more alpha-substituted vinyl monomer can be prepared which possesses a vinyl end group derived exclusively from the monosubstituted vinyl monomer. 
Macromonomers of structure 1 have application in the synthesis of block and graft copolymers. For examples of this utility, see U.S. Pat. No. 5,362,826 and WO 96/15157. xe2x80x9cOne potxe2x80x9d procedures for sequential macromonomer and block or graft copolymer synthesis are also within the scope of this invention.